The demand for improved network coverage and increased capacity and bandwidth for both voice and data services in wireless communication systems has led to continuous developments of radio access technologies (RATs) including, but not limited to, Global System for Mobile communication (GSM), Wideband Channel Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) including High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) with their respective multicarrier counterparts, Long Term Evolution (LTE) including support for carrier aggregation in Release 10 (R10), IEEE 802.11b/a/g/n, IEEE 802.16a/e, IEEE 802.20, cdma2000 1x, cdma2000 EV-DO.
The Third Generation Partnership Project (3GPP) WCDMA Release 8 (R8) introduced support for simultaneous use of two HSDPA downlink carriers (2C-HSDPA) to improve bandwidth usage with frequency diversity and resource pooling. 3GPP Release 9 (R9) introduced support for multiple-input multiple-output (MIMO) to the multicarrier downlink WCDMA. 3GPP R9 also introduced support for two HSUPA uplink carriers. 3GPP R10 introduced support for up to 4 downlink carriers (4C-HSDPA). This may be increased to up to 8 downlink carriers (8C-HSDPA) in 3GPP Release 11 (R11).
3GPP LTE R10 introduced support for simulaneous transmission and/or reception using the radio resources of a plurality of component carriers between a network node (i.e., evolved NodeB (eNB)) and a mobile terminal (i.e., wireless transmit/receive unit (WTRU)) within the same transmission interval. R10 HSPA with MIMO offers downlink peak data rates of 42 Mbps, while R10 multicarrier HSPA may further increase the peak rate by introducing support for up to four downlink component carriers. LTE R8/9 offers up to 100 Mbps in the single carrier downlink, while LTE R10 with (intra-RAT) carrier aggregation may further increase the peak rate by combining transmission resources of up to 5 component carriers.
Spectrum is a costly resource and not all frequency bands may be available to all operators. While many operators may offer support for both HSPA and LTE services, carrier aggregation may be limited to 2-3 component carriers per RAT for a given operator. In addition, legacy deployments may be maintained for a foreseeable future while LTE is being deployed. This may lead to a situation where operators may see periods of underutilization of radio resources/spectrum and capacity in one of their RATs.